Chromium (VI) detoxification by oxidation and flocculation of exopolysaccharides from Arthrobacter sp. B4

The exopolysaccharides from Arthrobacter sp. B4 (B4-EPS) exhibited an excellent chromium (VI) (Cr(VI)) removal capability without any pH adjustment, whereby 50 mg L−1 of Cr(VI) could be completely removed by 4 g L−1 of B4-EPS. The kinetics tests revealed that the first-order rate constant was 8.3 × 10−5 s−1 and the optimal reaction time was 720 min. However, a low initial concentration of Cr(VI) (5-30 mg L−1) would accelerate the reaction rate of Cr(VI) removal and shorten reaction time to less than 360 min. Meanwhile, the X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible (UV-vis) spectra indicated that Cr(VI) was reduced to Cr(III) by B4-EPS in accordance with the emergence of the green reaction products. Furthermore, the Fourier transform-infrared spectra (FT-IR) and nuclear magnetic resonance (NMR) showed that carboxyl and hydroxyl groups of B4-EPS contributed to Cr(VI) reduction. Additionally, a feasible scheme for Cr(VI) detoxification by oxidation and flocculation of B4-EPS is presented.